1. Field of the Invention
The present invention relates to a voltage-driven power semiconductor device constituted by press-contacting and connecting a plurality of voltage-driven power semiconductor elements parallel to each other and, more particularly, to an internal package structure and connection method for a voltage-driven power semiconductor device using a power semiconductor element with an enhanced emitter-side carrier accumulation effect.
2. Discussion of the Background
The power semiconductor device has widely been used for power conversion and power control of an inverter, a converter, and the like, and is indispensable in the field of power applications. In recent years, the power semiconductor device is required to attain a large capacity and a high switching speed along with a large power capacity and RF switching.
An example of a large-capacity power semiconductor device is a current-driven power semiconductor device represented by a gate turn-off thyristor (to be referred to as a GTO hereinafter). However, the GTO poses problems in device downsizing, RF switching, and the like. Instead, voltage-driven power semiconductor devices represented by an insulated gate bipolar transistor (to be referred to as an IGBT hereinafter) are being popular.
However, the IGBT has not attained a capacity as large as the capacity of the GTO. For this reason, an injection enhanced gate transistor (to be referred to as an IEGT hereinafter) has recently been developed as a large-capacity voltage-driven power semiconductor device capable of performing RF switching, and receives a great deal of attention as a post GTO.
A conventional press-contacting electrode type IEGT package will be explained. FIG. 1 is a sectional view showing an example of the conventional press-contacting electrode type IEGT package structure. FIG. 2 is a circuit diagram showing the electrical arrangement of the press-contacting electrode type IEGT package. The broken line B in FIGS. 1 and 2 indicates a portion corresponding to the IEGT package.
As shown in FIGS. 1 and 2, power semiconductor elements (IEGT chips) 300a to 300d and a free wheeling diode (to be referred to as an FWD hereinafter) chip 310a are press-contacted from the top by a collector (anode) press-contacting electrode plate 330 and from the bottom by an emitter (cathode) press-contacting electrode plate 340 via molybdenum plates 320a to 320f.
Copper posts respectively press-contacting the IEGT chips 300a to 300d have gate pins 350a to 350d. The gate pins 350a to 350d are connected by a gate line 370 to a gate circuit 360 outside the press-contacting electrode type IEGT package. The gate circuit 360 is connected to the emitter press-contacting electrode plate 340 by an emitter line 380.
The press-contacting electrode type IEGT package having this structure can advantageously decrease the inductance component of a connection medium between the collector press-contacting electrode plate (external terminal) 330 and the collectors of the IEGT chips 300a to 300d. Similarly, it can decrease the inductance component of a connection medium between the emitter press-contacting electrode plate (external terminal) 340 and the emitters of the IEGT chips 300a to 300d.
The IEGT chip has a gate resistor with a relatively large resistance value in order to suppress a turn-off voltage change (dv/dt). Accordingly, in the IEGT chip, the gate current is small, and the Miller effect time is long. The resistance value of the gate resistor is set to satisfy the following relation: IEGT chip element active area [cm.sup.2 ].times.Rg [.OMEGA.]&gt;20. Further, the IEGT has a much larger MOS gate electrostatic capacitance than the IGBT, and greatly changes in capacity with a collector-emitter voltage Vce.
IEGT chips, therefore, significantly differ in input capacity upon reception of an OFF signal at the gate owing to a slight difference in reverse charging of the input capacity just before an OFF operation. The gate voltages of the IEGT chips oscillate. The oscillating gate voltage greatly oscillates the IEGT element current to cause a steep current change (di/dt) in an OFF operation. This current changes may cause an abrupt voltage change (dv/dt) to destruct the IEGT chip.
The IEGT has a much higher energization ability than the IGBT. For this reason, when an excessive element current flows to cause, e.g., short-circuiting, the IEGT must be protected more reliably than the IGBT from the excessive current in order to prevent serious damage.